When a target appears in the same location as a previous cue, responding is typically delayed if the cue-target interval is relatively long. This phenomenon is termed inhibition of return (IOR) and has been suggested to reflect an attentional bias against a previously attended location in favor of novel visual space. It has been demonstrated in a recent study (Bao & Pöppel, 2007) that IOR is much stronger in the far periphery than in the perifoveal visual field, and this eccentricity effect is a very stable one that is resistant to practice (Bao et al., 2011). However, one factor that has not been considered in these previous studies is cortical magnification, since identical stimuli were used for different eccentricities. It is known that cortical representation of a unit area in the visual field decreases with eccentricity. Such a basic visual constraint might also account for the eccentricity effect of IOR. In order to clarify this possibility, the present study examined the IOR effects at both 7° and 21° eccentricities with the same spatial cueing paradigm in two critical conditions: in the same-size condition, identical stimuli were used for both eccentricities; in the size-scaling condition, stimuli were scaled according to the magnification factor so that they were larger at 21° than at 7° eccentricity. Compared to the same-size condition, size-scaling eliminated the difference in overall reaction times between the two eccentricities; however, IOR at 21° was still much stronger than that at 7°, showing exactly the same eccentricity effect in both conditions. These results revealed a robust eccentricity effect of IOR which could not be explained by the cortical magnification factor. Neural mechanisms underlying this effect are possibly related to subcortical contribution such as the involvement of superior colliculus.